The Laboratory is developing methods to examine the intra-individual genomic somatic heterogeneity. These studies are being performed on normal and diseased tissue. Since the mitochondrial genome is the main site of oxidation and the generation of free radicals and there are few, if any, repair mechanisms for the mit-DNA, we suspect that there may be a significant level of somatic mutations in certain postmitotic tissues. The mitochondrial genome in tissues under oxidative stress, such as the brain and muscle, may be the most vulnerable to mutagenesis. To study this possibility, the Laboratory has developed a rapid method of DNA sequencing by employing the polymerase chain reaction and an amplification primer with a 5' biotinylated ligand. This provides a simplified method of preparing singLe stranded DNA which is easily sequenced by the Sanger technique. This procedure has facilitated molecular studies of the mit-genome and should prove general[y useful for the study and diagnosis of human genetic diseases. When restriction fragment analysis was first applied to the mitochondrial genome, it was concluded that the genome was monoclonal in each individual with LittLe evidence of somatic mutations. However, over the past several years, heteroplasmy of the michochondrial genome has been documented. Large (7kb) deletion mutations have been observed in the muscle mitochondria, whereas, the leukocyte mitochondria were intact in individuals with mitochondrial myopathies and related clinical disorders. The Laboratory is examining the relationship between heteroplasmy and the aging process using widely spaced primer (WISP) PCR. Mutational events in the mitochondrial genome may provide s explanations for the pathophysiology associated with certain diseases and aging. In an effort to identify disease susceptibility loci by means of whole genome screening, the Laboratory is conducting genetic linkage analysis studies in families with major psychiatric disorders. Working collaboratively, we are using highly polymorphic dinucleotide (CA) repeat markers to examine extended pedigrees.